Xdpyinfo is a utility for displaying information about an X
server. It is used to examine the capabilities of a server, the predefined
values for various parameters used in communicating between clients and
the server, and the different types of screens and visuals that are available.

By default, numeric information (opcode, base event, base error) about
protocol extensions is not displayed. This information can be obtained
with the -queryExtensions option. Use of this option on servers that dynamically
load extensions will likely cause all possible extensions to be loaded,
which can be slow and can consume significant server resources.

Detailed
information about a particular extension is displayed with the -extextensionName
option. If extensionName is all, information about all extensions supported
by both xdpyinfo and the server is displayed.